NEW YORK -- The NHL and the NHL Players' Association met with a federal mediator Wednesday in an attempt to resolve the lingering labor dispute that has jeopardized the 2012-13 season.

The two sides met at an undisclosed location for approximately six hours and are meeting with mediators again Thursday in Iselin, N.J., where there is a sub-regional FMCS office, a source told ESPN.com. Thursday's meeting began at 11 a.m.

Details about the initial meeting were scarce -- the league and union are trying to remain relatively tight-lipped -- but it is believed both sides spent large amounts of time in separate sessions with a mediator to discuss their bargaining position.

Assigned to facilitate what has become a contentious standoff, the Federal Mediation and Conciliation Services has been tasked with trying to forge common ground between the league and the union. The two sides remain divided on key issues, such as division of revenue and player-contracting rights, although any decision rendered will be non-binding.

"A small group of NHLPA staff and players met today with two experienced FMCS mediators. We expect that these discussions will resume Thursday," NHLPA executive director Donald Fehr said in a union-issued statement.

The two sides had not met for a formal negotiation session since last Wednesday, when the NHL rejected the union's latest proposal.

Multiple sources told ESPN that both sides are not overly optimistic that an agreement will be reached through mediation.

The FMCS, which was involved in recent labor disputes for both the NBA and NFL, was employed during the NHL's last work stoppage in 2004-05, but the season was canceled nonetheless.

FMCS director George Cohen originally assigned three mediators to help with negotiations -- deputy director Scot L. Beckenbaugh, director of mediation services John Sweeney and commissioner Guy Serota.

Serota, however, was removed from the case less than an hour after the announcement because of questionable activity from his personal Twitter account -- he told ESPN that his account was hacked -- so as to "dispel any cloud on the mediation process," according to Cohen.

The NHL already has canceled all regular-season games through Dec. 14 -- as well as marquee events such as the Winter Classic and the All-Star Game -- as the lockout has stretched into its 10th week. Many fear the cancellation of the entire season may be next.

With time running out and no agreement in sight, decertification was an option discussed within the union's ranks during the past week. Although the two sides chose to explore a different route in mediation, decertification is not off the table, according to a source.

It is not immediately clear if the league and union will meet with the FMCS beyond Wednesday. The next known significant date is Dec. 5, when the NHL's board of governors are slated to meet in New York for an internal meeting on the current state of affairs.